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transport across cell membranes Flashcards

1
Q

What are plasma membranes?

A

All membranes around and within all cells

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2
Q

What is the cell-surface membrane?

A

Name given to the plasma membrane that surrounds cells and forms and forms a boundary between the cytoplasm and the environment

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3
Q

What does the cell-surface membrane control?

A

Controls the movement of substances in and out of the cell

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4
Q

What are the 5 important components of the cell-surface membrane?

A

Phospholipids
Proteins
Cholesterol
Glycolipids
Glycoproteins

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5
Q

Why are phospholipids important components of the cell-surface membrane?

A

-The hydrophilic heads of both the layers point to the outside of the cell-surface membrane and the hydrophobic tails point to the centre.

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6
Q

What kind of material can move through the membrane via the phospholipid portion?

A

Lipid-soluble material

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7
Q

What are the 3 functions of phospholipids in the membrane?

A
  1. Allows lipid-soluble substances to enter and leave the cell
  2. Prevents water-soluble substances entering and leaving the cell
  3. Makes the membrane flexible and self-sealing
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8
Q

How are proteins spread about the cell-surface membrane?

A

Interspersed

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9
Q

What are the functions of proteins that are embedded in the cell-surface membrane?

A

They give mechanical support to the membrane or as cell receptors for molecules such as hormones

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10
Q

Which proteins span the cell-surface membrane?

A

Some proteins span the bilayer. Some of these are protein channels, which form water-filled tubes to allow water-soluble ions to diffuse across the membrane.

Others are carrier proteins that bind to ions or molecules like glucose and amino acids, then change shape in order to move these molecules across the membrane

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11
Q

What are the 6 different functions of proteins in the membrane?

A

Provide structural support

Act as channels transporting water-soluble substances across the membrane

Allow active transport across the membrane through carrier proteins

Form cell-surface receptors for identifying cells

Help cells adhere together

Act as receptors for molecules such as hormones

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12
Q

What are glycolipids made up of?

A

A carbohydrate covalently bonded with a lipid

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13
Q

How far does the carbohydrate portion of a glycolipid extend?

A

From the phospholipid bilayer into the watery environment outside the cell where it acts as a cell-surface receptor for specific chemicals.

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13
Q

What are the functions of glycolipids in the membrane?

A

Act as recognition sites

Help maintain the stability of the membrane

Help cells attach to one another and so form tissues

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14
Q

What do glycoproteins act as?

A

Cell surface receptors, specifically for hormones and neurotransmitters

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15
Q

What are the functions of glycoproteins in the membrane?

A

Act as recognition sites

Help cells attach to one another and so form tissues

Allows cells to recognise one another, for example lymphocytes can recognise an organisms own cells

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16
Q

What is the primary function of the cell-surface membrane?

A

Controls the movement of substances into and out of the cell

This includes regulating the entry and exit of materials in organelles.

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17
Q

What role do membranes play in organelles like mitochondria and chloroplasts?

A

Separate organelles from cytoplasm for specific metabolic reactions

This allows distinct processes to occur without interference.

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18
Q

What internal transport system is provided by membranes within cells?

A

Endoplasmic reticulum

It functions as a transport network for materials within the cell.

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19
Q

How do membranes isolate potentially damaging enzymes?

A

By containing lysosomes

This prevents the enzymes from damaging the cell’s other structures.

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20
Q

What surfaces do membranes provide for cellular reactions?

A

Surfaces for reactions such as protein synthesis

Ribosomes on rough endoplasmic reticulum facilitate this process.

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21
Q

Fill in the blank: The permeability of the cell-surface membrane is affected by the _______.

A

[named variable]

This variable could be temperature, pH, or another factor affecting membrane permeability.

22
Q

What are the three main reasons most molecules do not freely diffuse across the cell-surface membrane?

A
  1. Not soluble in lipids
  2. Too large to pass through channels
  3. Same charge as the protein channels

These factors hinder the ability of molecules to cross the membrane.

23
Q

What is the fluid-mosaic model of the cell-surface membrane?

A

A model describing the flexible structure of the membrane with varying protein shapes and sizes

‘Fluid’ refers to the movement of phospholipids; ‘mosaic’ refers to the diverse proteins embedded.

24
Q

Why is the term ‘fluid’ used in the fluid-mosaic model?

A

Individual phospholipid molecules can move relative to one another

This movement allows the membrane to be flexible and change shape.

25
Q

What is the function of glycoproteins in the cell-surface membrane?

A

Act as recognition sites for chemicals, e.g., hormones

26
Q

What role does cholesterol play in the cell-surface membrane?

A

Adds strength to the membrane

Cholesterol helps maintain membrane integrity and fluidity.

27
Q

What is the definition of diffusion?

A

The net movement of molecules or ions from a region where they are more highly concentrated to one where their concentration is lower until evenly distributed.

28
Q

What type of transport is diffusion classified as?

A

Passive transport.

29
Q

What energy source is necessary for diffusion?

A

No external source of energy is required; the motion comes from the kinetic energy of the particles.

30
Q

What are the characteristics of particles in diffusion?

A

Particles are constantly in motion, with random movement and no set pattern.

31
Q

Which molecules can easily diffuse across cell membranes?

A

Small, non-polar molecules such as oxygen and carbon dioxide.

32
Q

What is facilitated diffusion?

A

A passive process that helps charged ions and polar molecules diffuse across membranes via transmembrane channels and carriers.

33
Q

What is the main difference between diffusion and facilitated diffusion?

A

Facilitated diffusion occurs at specific points on the plasma membrane and involves protein channels and carriers.

34
Q

What type of molecules do not diffuse easily across plasma membranes?

A

Charged ions and polar molecules.

35
Q

What is the role of transmembrane proteins in facilitated diffusion?

A

They facilitate the movement of molecules that cannot easily pass through the membrane.

36
Q

True or False: Diffusion requires an external input of ATP.

A

False.

37
Q

Fill in the blank: Diffusion occurs down a _______.

A

concentration gradient.

38
Q

What happens to particles concentrated in one part of a closed vessel during diffusion?

A

They distribute themselves evenly throughout the vessel.

39
Q

What is the kinetic energy’s role in diffusion?

A

It causes particles to move randomly, allowing diffusion to occur.

40
Q

What are the two types of proteins involved in facilitated diffusion?

A
  • Protein channels
  • Carrier proteins
41
Q

What is a key hint to remember about diffusion?

A

Diffusion is the net movement of particles; more move in one direction than in another due to concentration differences.

42
Q

Fill in the blank: Diffusion only occurs between different concentrations of the _______.

A

same substance.

43
Q

What are protein channels?

A

Proteins that form water-filled openings in the membrane, allowing specific water-soluble ions to pass through

They are selective, opening only in the presence of specific ions.

44
Q

How do protein channels control ion movement?

A

They remain closed if the specific ion is not present, controlling the entry and exit of ions

Ions bind to the channel, causing it to close to one side of the membrane.

45
Q

What is the role of hydrophilic channels?

A

They facilitate the passage of water-soluble ions through the membrane

Hydrophilic properties attract water and ions.

46
Q

What are carrier proteins?

A

Proteins that span the plasma membrane and assist in the facilitated diffusion of molecules

They change shape to transport specific molecules.

47
Q

How do carrier proteins facilitate the transport of glucose?

A

When glucose binds to the carrier protein, it causes the protein to change shape and release glucose inside the membrane

This process does not require external energy.

48
Q

What is facilitated diffusion?

A

A process where molecules move from an area of high concentration to an area of low concentration without energy

Utilizes the kinetic energy of the molecules.

49
Q

Fill in the blank: Protein channels are _______ to specific ions.

A

selective

50
Q

True or False: Carrier proteins require external energy to transport molecules.

A

False

They operate using the kinetic energy of the molecules.

51
Q

What triggers the opening of a protein channel?

A

The presence of a specific ion

This selectivity ensures proper ion regulation.

52
Q

What happens to a carrier protein when a specific molecule binds to it?

A

It changes shape to release the molecule inside the membrane

This is a key mechanism in facilitated diffusion.

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